She was born in the year 2907 of the Third Age. She was the daughter of Dírhael and Ivorwen, and a descendent of chieftain Aranarth. Her father at first did not want her to marry Arathorn II, partly because she was at the time younger than customary for marriage, and he also foresaw that Arathorn would have a short life. However Ivorwen persuaded him in the end, saying that Arathorn's short life was a further incentive to have a quick marriage, so that an heir could be born to be their people's leader.

Gilraen's son Aragorn was born in 2931 Third Age, but her husband died two years later. She then brought her son to live in Imladris. She opposed Aragorn's love for Arwen, believing that Arwen's lineage was more noble than his and that Elves and mortals should not intermarry. In later years Gilraen returned to her people where she died in 3007, aged one-hundred years. Her final words to Aragorn were "Ónen i-Estel Edain, ú-chebin estel anim" meaning "I gave Hope (an obvious reference to her son's nickname) to the Dúnedain, I have kept no hope for myself."

In the Extended Edition of Peter Jackson's The Fellowship of the Ring, Aragorn and Elrond have a conversation at a memorial to Gilraen in Rivendell. Elrond suggests that she brought Aragorn to Imladris for safety from pursuit by the forces of evil. Elrond also thinks that Gilraen believed Aragorn would not escape his fate. Her memorial features a statue along with her name and an inscription of her final words written in Tengwar.

In Peter Jackson's The Return of the King, Elrond and Aragorn recite Gilraen's final words when Elrond brings the re-forged sword Anduril to Aragorn, with the words possibly taking on a different connotation from their meaning in the book.